In the early part of the 20th century, geologists studied the vibrations (seismic waves) generated by earthquakes to learn more about the structure of the earth's interior. They discovered that it is made up of these distinct layers: the crust, the mantle, and the core.
Core
The core is also divided into two regions, the inner core and the outer core. The the outer core is liquid iron and the inner core is solid iron and nickel. The outer core is made of iron and is very dense. Scientists hypothesize that the circulation and movement of the outer core causes the magnetic field around the earth. It is believed to be circulating in the counter-clockwise direction giving us the north pole in its present location. It switches about every million years or so. A record of this "switching" is recorded in the rocks both on land and in the ocean crust.
Mantle
The Earth's mantle is a roughly 1,800 mile (2,900 km) thick shell of dense compressed super heated molten or liquid rock located between the lithosphere and outer core. The mantle is the Earth's thickest layer making up 70% of Earth's volume.
Lithosphere
In plate tectonics, the actual plate is made up of the crust and upper most mantle. Scientists call this layer the LITHOSPHERE. It is the rigid outermost shell of a rocky planet. Here on Earth the lithosphere contains the crust and upper mantle. The Earth has two types of lithosphere: oceanic and continental. The lithosphere is broken up into tectonic plates.
Crust
The Crust--The outer skin of the planet is composed of igneous, metamorphic, and sedimentary rock. The crust is divided into continental or oceanic based on composition and formation. Continental crust is comprised or made of mostly the igneous rock granite, the continental crust is relatively thick compared to the oceanic crust with a depth that ranges from 30 km to 50 km. The density of continental crustal rock is 2.7g/mL. Oceanic crust is thinner than the continental crust. Oceanic crustal rocks are composed mainly of the igneous rock basalt, and are mafic in composition. The average specific gravity of oceanic crustal rock is 3.0 g/mL.
Alfred Wegener and Continental Drift
Alfred Wegener proposed the theory of continental drift at the beginning of the 20th century. His theory of Continental Drift stated that the Earth's continents were once joined together, but gradually moved apart over millions of years. It offered an explanation of the existence of similar fossils and rocks on continents that are far apart from each other. But it took a long time for the idea to become accepted by other scientists. Wegener’s evidence for continental drift was that:
The same types of fossilized animals and plants (Glossopteris, Mesosaurus, Cygnognathus, Lystrosaurus) are found in South America and Africa
The shape of the east coast of South America fits the west coast of Africa, like pieces in a jigsaw puzzle
Matching rock formations and mountain chains are found in South America and Africa
Pangaea
By 1922 Wegener put forward his theory of a supercontinent. Using geological evidences Wegener proposed that approximately 300 million years ago all the continents were joined as a supercontinent. Wegener named this supercontinent Pangaea (all lands). About 200 million years ago the supercontinent began to break up and the small continents moved to their present day positions. Wegener proposed that the continents floated in a similar way to icebergs on water. Wegener’s explanation was that the continents were mainly made up of granite a less dense rock compared to the basalt that makes up the sea floor. It is this density difference which allows the continents to drift and float, break apart and converge. Wegener proposed the forces responsible for continental drift were due to centrifugal force of the rotating Earth and the gravitational pull from the sun and the moon. Wegener's theory was harshly rejected by most scientists at the time. This was mainly due to Wegener’s limited explanation as to the mechanisms responsible for moving the continents.
Harry Hess and Seafloor Spreading
Remember, Alfred Wegener's theory of Continental Drift was rejected by fellow scientists of his time. It would take a discovery by another scientist, Harry Hess in the 1950's to help prove Alfred Wegener's theory of Continental Drift to be TRUE. What harry Hess discovered was the Earth's longest mountain range. This mountain is deep underwater and makes it's way throughout the worlds oceans. The Ocean Ridge system, seen to the right winds and snakes its way between the continents, and is more than 56,000 kilometers (35,000 mi) long. The Mid-Ocean Ridge system is a continuous chain of underwater volcanic mountains that extends through out the world's oceans. What Harry Hess realized and discovered was that the seafloor is actually moving apart at these ocean ridges. Seafloor spreading takes place at ocean ridges and produces basalt, the rock that makes up the oceanic crust.
It is here, at Mid-Ocean Ridges, that new sea-floor crust is produced and much of the earth’s internal heat is released. At Mid-Ocean Ridges, two plates are pulling apart from each other as hot magma (liquid rock) emerges from the mantle and oozes forth as lava to fill the crack continuously created by plate separation. The lava cools and attaches itself to the trailing edge of each plate, forming new ocean floor crust in a process commonly known as sea-floor spreading. This eventually lead to the theory of Sea floor spreading which states that magma from the Earth's interior rises to the surface at Mid-Ocean ridges and cools to form new seafloor, spreading the seafloor apart in two directions.
Magnetic Clues
The theory of seafloor spreading was later confirmed by the measurement of magnetic anomalies in ocean floor rocks. When molten lava is expelled from an ocean ridge, it creates new ocean floor. The magma (the hot, liquid rock) then cools and elements within the rock line up with the planet’s prevailing magnetic field, retaining the orientation present at that time. Since the planet’s magnetic field changes over time, evidence of this would show up in the ocean floor rocks.In rocks from the ocean floor, scientists discovered a pattern of stripes representing these magnetic anomalies—providing a record of the changes in the orientation of the magnetic field over time. These patterns spread out symmetrically on either side of the Mid-Atlantic Ridge, a long chain of volcanic mountains cutting through the center of the Atlantic Ocean. Scientists concluded that the pattern and distribution of these rock stripes, showing the magnetic field reversals over time, could only have occurred if the seafloor had been spreading apart over millions of years.
A New Theory Emerges: Plate Tectonics
With Seafloor Spreading and Continental Drift, scientists were now convinced that the Earth's Crust and continents do move. This lead to the emergence of a new theory. By the 1960's scientists combined the theories of Continental Drift and Seafloor Spreading to make a new theory: PLATE TECTONICS. The theory of Plate Tectonics states that Earth's crust is broken up into sections or plates that slowly move over time; and that the movement of these plate are responsible for the creation of Volcanoes, Earthquakes, and Mountains. This is the most important theory in the Geosciences because it explain why our Earth isn't flat, but has mountains, Earthquakes, and active volcanoes. Of these plates, there are a few handfuls of major plates and dozens of smaller, or minor, plates. Six of the majors are named for the continents embedded within them, such as the North American, African, and Antarctic plates. Though smaller in size, the minors are no less important when it comes to shaping the Earth. The tiny Juan de Fuca plate is largely responsible for the volcanoes that dot the Pacific Northwest of the United States.
The plates make up Earth's outer shell, are called the lithosphere. (includes the crust and uppermost part of the mantle.) Moving currents of hot molten rocks below these plates propel them along like a jumble of conveyor belts in disrepair. Most geologic activity stems from the interaction from where these plates meet.
The movement of the plates creates three types of tectonic boundaries: convergent, where plates move into one another; divergent, where plates move apart; and transform, where plates move sideways in relation to each other. These plate boundaries create many of the world's great mountain chains and regions on intense volcanic and seismic (earthquake) activity. Click on the buttons below. What patterns or connection can you make between the locations of plate boundaries, Earthquakes, and Volcanoes? Next, see if you can drag the worlds plates to there proper locations
Plate Boundaries: Convergent, Divergent, and Transform
Plate Meet and interact in three general ways: Plate collide at Convergent Plate Boundaries, they spread or move apart at Divergent Plate Boundaries, and they slide past one another at Transform Plate Boundaries.
Convergent Plate Boundaries
Where plates serving landmasses collide, the crust crumples and buckles into mountain ranges. India and Asia crashed about 55 million years ago, slowly giving rise to the Himalaya, the highest mountain system on Earth. As the mash-up continues, the mountains get higher. Mount Everest, the highest point on Earth, may be a tiny bit taller tomorrow than it is today. These convergent boundaries also occur where a plate of ocean , in a process called subduction, under a landmass. As the overlying plate lifts up, it also forms mountain ranges. In addition, the diving plate melts and is often spewed out in volcanic eruptions such as those that formed some of the mountains in the Andes of South America.
At ocean-ocean convergences, one plate usually
dives beneath the other, forming deep trenches like the Mariana Trench in the North Pacific Ocean, the deepest point on Earth. These types of collisions can also lead to underwater volcanoes that eventually build up into island arcs like Japan. 3 Types of Convergent Plate boundaries:
Plates collide and smash together in a variety of ways. However, they all one thing in common, they all collide!!!!! The three types of collision are: Ocean plate collides with Continental plate (Ocean--><--Continent), Ocean plate collides with Ocean plate (Ocean--><--Ocean), and Continental plate collides with Continental plate (Continental--><--Continent).
Convergent: Ocean--><--Continent
When a Continental plate and an oceanic plate collide, they create a convergent plate boundary and a subduction zone. The oceanic plate sinks under the continental plate as it is denser. Remember, Continental crust or plate has a lower density and therefore floats higher than the heavier more dense oceanic crust. Because the oceanic plate or crust is heavier and more dense, the oceanic plate is forced underneath Continental plate creating what is known as a Subduction zone. As the oceanic crust subducts and gets forced underneath Continental crust, it melts underneath in the subduction zone due to the immense pressure and friction between the two plates. As a result the subducting plate or crust melts and becomes magma. This Magma is higher in temperature (hotter) and less dense than the surrounding rock and therefore floats to the surface through cracks and fissures. As the magma continues to rise up through the cracks, it escapes onto the surface and solidifies, building up chain of Volcanic Mountains at the surface of Earth over Millions of years. Magma on the surface is now known as lava. The converging of the oceanic and continental plate also cause deep oceanic trenches to form. The Andes Mountains in South America formed this way. The Andes Mountains are actually a series of volcanic Mountains that formed above a suduction zone between the Nazca and South American Plate. Convergent: Ocean--><--Ocean
When a Ocean plate and Ocean plate collide, a convergent plate boundary forms and a Subduction zone. The oceanic plate collides with oceanic, the more dense plate sinks and subducts the less dense crust or plate. The ocean crust with a lower density floats "higher" than the heavier more dense oceanic crust. Because the oceanic crust is heavier and more dense, the oceanic crust if forced underneath Continental crust creating what is know as a Subduction zone. Just like in the previous example, the more dense oceanic crust subducts and gets forced underneath, melting in the Subduction zone from the immense pressure and friction between the two plates. As a result the subducting plate or crust melts and becomes magma. This Magma higher is higher in temperature (hotter) and less dense than the surrounding rock and therefore floats to the surface through cracks and fissures. As the magma continues to rise up through the cracks,it escapes onto the surface and solidifies, building up chain of Volcanic Islands at the surface over Millions of years. Magma on the surface is now known as lava. The converging of the oceanic and continental plate also cause deep oceanic trenches to form. Japan, Indonesia, and the Marianas Islands are all examples of a chain of volcanic islands that formed at Ocean to Ocean convergent plate boundary.
Convergent: Continent--><--Continent
When two continents meet head-on, neither plate or crust is subducted because the continental rocks are relatively light and have the same density, like two colliding icebergs, these plates resist downward motion and therefore do not subduct. Instead, the crust tends to buckle and be pushed upward building mountains. The collision of India into Asia 40 million years ago caused the Eurasian Plate to crumple up and override the Indian Plate. After the collision, the slow continuous convergence of the two plates over millions of years pushed up the Himalayan Mountains to their present heights, creating the highest mountain in the world, Mount Everest.
Divergent Plate Boundaries
Remember the theory of Seafloor Spreading? After the the theory of Plate Tectonics, Seafloor Spreading became known as a Divergent Plate Boundary. Plates move apart or separate at divergent plate boundaries. At Divergent Boundaries in the oceans, magma from deep in the Earth's mantle rises toward the surface and pushes apart two or more plates. This process is what was responsible for breaking up Pangaea 250 millions years ago. Mountains and volcanoes rise along an underwater system of volcanoes called Ocean Ridges. These Ocean ridges are areas of new crust or plate creation. As you move farther from the ridge, rock becomes older. The mid-Atlantic Ocean ridge system is a perfect example of a divergent plate boundary.
This process creates new ocean floor rock at the ridges and pushes apart continents. A single mid-ocean ridge system connects the world's oceans, making the ridge the longest mountain range in the world. On land, divergent plate boundaries can break apart continents such as the Great Rift Valley in Africa, where plates are tugged apart. If the plates there continue to diverge, millions of years from now eastern Africa will split from the continent to form a new landmass. Eventually, East will be ripped apart from the rest of the African Continent, creating a linear sea and one day an ocean. A mid-ocean ridge would then mark the boundary between the plates. At almost every Divergent Plate boundary you find features such as Ocean ridges or a long continuous Valley know as rift valley. Active volcanism (volcanoes) occur at divergent plate boundaries along with frequent earthquakes.
Transform Plate Boundaries
The San Andreas Fault in California is an example of a Transform Plate Boundary, where two plates grind past each other along what are called strike-slip faults. At the San Andreas Transform plate Boundary, The pacific Plate grinds or slides past the North American Plate. These boundaries don't spectacular features like mountains, volcanoes, trenches or oceans, but the halting motion often triggers large earthquakes, such as the 1906 one that devastated San Francisco. If one one considers the current direction of movement, as these plates continue to slide past one another, eventually the city of Los Angeles will be pushed up along side the city of San Francisco millions of years in the future. At almost every Transform plate boundary, you get features such as Mountains and Earthquakes. Without Plate Tectonics, the world would have no mountains, earthquakes, or volcanoes; the world would essentially be flat and featureless
Rafts of Rock
If you recall Alfred Wegener could not explain how continents or plates moved; and therefore his theory was rejected by fellow scientists. So what force could possibly be strong enough to move continents and the outer crust of our Earth? The answer come from heat within our Earth. Heat from the core fuelsor drives plate tectonics. Convection in the Mantle causes creates areas within our Earth' s where hot low density molten rock (magma) rises in certain locations, moving these plate the plates like giant rafts of rock. What goes up must come down right? Well, if you consider a lava lamp, as the that heated lava rises, eventually it will cool and sink back down. The same process happens within our Earth. Eventually this molten high density rock (magma) will cool and sink back down. This rising and sinking process creates convection currents within our Earth's mantle, a force strong enough to move plate, build mountains, release Earthquakes, and fuel the Volcanoes through our world.
Project PLATE TECTONICS
Layers of the Earth
In the early part of the 20th century, geologists studied the vibrations (seismic waves) generated by earthquakes to learn more about the structure of the earth's interior. They discovered that it is made up of these distinct layers: the crust, the mantle, and the core.
Core
The core is also divided into two regions, the inner core and the outer core. The the outer core is liquid iron and the inner core is solid iron and nickel. The outer core is made of iron and is very dense. Scientists hypothesize that the circulation and movement of the outer core causes the magnetic field around the earth. It is believed to be circulating in the counter-clockwise direction giving us the north pole in its present location. It switches about every million years or so. A record of this "switching" is recorded in the rocks both on land and in the ocean crust.Mantle
The Earth's mantle is a roughly 1,800 mile (2,900 km) thick shell of dense compressed super heated molten or liquid rock located between the lithosphere and outer core. The mantle is the Earth's thickest layer making up 70% of Earth's volume.Lithosphere
In plate tectonics, the actual plate is made up of the crust and upper most mantle. Scientists call this layer the LITHOSPHERE. It is the rigid outermost shell of a rocky planet. Here on Earth the lithosphere contains the crust and upper mantle. The Earth has two types of lithosphere: oceanic and continental. The lithosphere is broken up into tectonic plates.Crust
The Crust--The outer skin of the planet is composed of igneous, metamorphic, and sedimentary rock. The crust is divided into continental or oceanic based on composition and formation. Continental crust is comprised or made of mostly the igneous rock granite, the continental crust is relatively thick compared to the oceanic crust with a depth that ranges from 30 km to 50 km. The density of continental crustal rock is 2.7g/mL. Oceanic crust is thinner than the continental crust. Oceanic crustal rocks are composed mainly of the igneous rock basalt, and are mafic in composition. The average specific gravity of oceanic crustal rock is 3.0 g/mL.Alfred Wegener and Continental Drift
Alfred Wegener proposed the theory of continental drift at the beginning of the 20th century. His theory of Continental Drift stated that the Earth's continents were once joined together, but gradually moved apart over millions of years. It offered an explanation of the existence of similar fossils and rocks on continents that are far apart from each other. But it took a long time for the idea to become accepted by other scientists. Wegener’s evidence for continental drift was that:Pangaea
By 1922 Wegener put forward his theory of a supercontinent. Using geological evidences Wegener proposed that approximately 300 million years ago all the continents were joined as a supercontinent. Wegener named this supercontinent Pangaea (all lands). About 200 million years ago the supercontinent began to break up and the small continents moved to their present day positions. Wegenerproposed that the continents floated in a similar way to icebergs on water. Wegener’s explanation was that the continents were mainly made up of granite a less dense rock compared to the basalt that makes up the sea floor. It is this density difference which allows the continents to drift and float, break apart and converge. Wegener proposed the forces responsible for continental drift were due to centrifugal force of the rotating Earth and the gravitational pull from the sun and the moon. Wegener's theory was harshly rejected by most scientists at the time. This was mainly due to Wegener’s limited explanation as to the mechanisms responsible for moving the continents.
Harry Hess and Seafloor Spreading
Remember, Alfred Wegener's theory of Continental Drift was rejected by fellow scientists of his time. It would take a discovery by another scientist, Harry Hess in the 1950's to help prove Alfred Wegener's theory of Continental Drift to be TRUE. What harry Hess discovered was the Earth's longest mountain range. This mountain is deep underwater and makes it's way throughout the worlds oceans. The Ocean Ridge system, seen to the right winds and snakes its way between the continents, and is more than 56,000 kilometers (35,000 mi) long. The Mid-Ocean Ridge system is a continuous chain of underwater volcanic mountains that extends through out the world's oceans. What Harry Hess realized and discovered was that the seafloor is actually moving apart at these ocean ridges. Seafloor spreading takes place at ocean ridges and produces basalt, the rock that makes up the oceanic crust.It is here, at Mid-Ocean Ridges, that new sea-floor crust is produced and much of the earth’s internal heat is released. At Mid-Ocean Ridges, two plates are pulling
apart from each other as hot magma (liquid rock) emerges from the mantle and oozes forth as lava to fill the crack continuously created by plate separation. The lava cools and attaches itself to the trailing edge of each plate, forming new ocean floor crust in a process commonly known as sea-floor spreading. This eventually lead to the theory of Sea floor spreading which states that magma from the Earth's interior rises to the surface at Mid-Ocean ridges and cools to form new seafloor, spreading the seafloor apart in two directions.
Magnetic Clues
The theory of seafloor spreading was later confirmed by the measurement of magnetic anomalies in ocean floor rocks. When molten lava is expelled from an ocean ridge, it creates new ocean floor. The magma (the hot, liquid rock) then cools and elements within the rock line up with the planet’s prevailing magnetic field, retaining the orientation present at that time. Since the planet’s magnetic field changes over time, evidence of this would show up in the ocean floor rocks.In rocks from the ocean floor, scientists discovered a pattern of stripes representing these magnetic anomalies—providing a record of the changes in the orientation of the magnetic field over time. These patterns spread out symmetrically on either side of the Mid-Atlantic Ridge, a long chain of volcanic mountains cutting through the center of the Atlantic Ocean. Scientists concluded that the pattern and distribution of these rock stripes, showing the magnetic field reversals over time, could only have occurred if the seafloor had been spreading apart over millions of years.A New Theory Emerges: Plate Tectonics
With Seafloor Spreading and Continental Drift, scientists were now convinced that the Earth's Crust and continents do move. This lead to the emergence of a new theory. By the 1960's scientists combined the theories of Continental Drift and Seafloor Spreading to make a new theory: PLATE TECTONICS. The theory of Plate Tectonics states that Earth's crust is broken up into sections or plates that slowly move over time; and that the movement of these plate are responsible for the creation of Volcanoes, Earthquakes, and Mountains. This is the most important theory in the Geosciences because it explain why our Earth isn't flat, but has mountains, Earthquakes, and active volcanoes. Of these plates, there are a few handfuls of major plates and dozens of smaller, or minor, plates. Six of the majors are named for the continents embedded within them, such as the North American, African, and Antarctic plates. Though smaller in size, the minors are no less important when it comes to shaping the Earth. The tiny Juan de Fuca plate is largely responsible for the volcanoes that dot the Pacific Northwest of the United States.The plates make up Earth's outer shell, are called the lithosphere. (includes the crust and uppermost part of the mantle.) Moving currents of hot molten rocks below these plates propel them along like a jumble of conveyor belts in disrepair. Most geologic activity stems from the interaction from where these plates meet.
The movement of the plates creates three types of tectonic boundaries: convergent, where plates move into one another; divergent, where plates move apart; and transform, where plates move sideways in relation to each other. These plate boundaries create many of the world's great mountain chains and regions on intense volcanic and seismic (earthquake) activity. Click on the buttons below. What patterns or connection can you make between the locations of plate boundaries, Earthquakes, and Volcanoes? Next, see if you can drag the worlds plates to there proper locations
Plate Boundaries: Convergent, Divergent, and Transform
Plate Meet and interact in three general ways: Plate collide at Convergent Plate Boundaries, they spread or move apart at Divergent Plate Boundaries, and they slide past one another at Transform Plate Boundaries.Convergent Plate Boundaries
Where plates serving landmasses collide, the crust crumples and buckles into mountain ranges. India and Asia crashed about 55 million years ago, slowly giving rise to the Himalaya, the highest mountain system on Earth. As the mash-up continues, the mountains get higher. Mount Everest, the highest point on Earth, may be a tiny bit taller tomorrow than it is today. These convergent boundaries also occur where a plate of ocean , in a process called subduction, under a landmass. As the overlying plate lifts up, it also forms mountain ranges. In addition, the diving plate melts and is often spewed out in volcanic eruptions such as those that formed some of the mountains in the Andes of South America.
At ocean-ocean convergences, one plate usually
dives beneath the other, forming deep trenches like the Mariana Trench in the North Pacific Ocean, the deepest point on Earth. These types of collisions can also lead to underwater volcanoes that eventually build up into island arcs like Japan.
3 Types of Convergent Plate boundaries:
Plates collide and smash together in a variety of ways. However, they all one thing in common, they all collide!!!!! The three types of collision are: Ocean plate collides with Continental plate (Ocean--><--Continent), Ocean plate collides with Ocean plate (Ocean--><--Ocean), and Continental plate collides with Continental plate (Continental--><--Continent).
Convergent: Ocean--><--Continent
When a Continental plate and an oceanic plate collide, they create a convergent plate boundary and a subduction zone. The oceanic plate sinks under the continental plate as it is denser. Remember, Continental crust or plate has a lower density and therefore floats higher than the heavier more dense oceanic crust. Because the oceanic plate or crust is heavier and more dense, the oceanic plate is forced underneath Continental plate creating what is known as a Subduction zone. As the oceanic crust subducts and gets forced underneath Continental crust, it melts underneath in the subduction zone due to the immense pressure and friction between the two plates. As a result the subducting plate or crust melts and becomes magma. This Magma is higher in temperature (hotter) and less dense than the surrounding rock and therefore floats to the surface through cracks and fissures. As the magma continues to rise up through the cracks, it escapes onto the surface and solidifies, building up chain of Volcanic Mountains at the surface of Earth over Millions of years. Magma on the surface is now known as lava. The converging of the oceanic and continental plate also cause deep oceanic trenches to form. The Andes Mountains in South America formed this way. The Andes Mountains are actually a series of volcanic Mountains that formed above a suduction zone between the Nazca and South American Plate.
Convergent: Ocean--><--Ocean
When a Ocean plate and Ocean plate collide, a convergent plate boundary forms and a Subduction zone. The oceanic plate collides with oceanic, the more dense plate sinks and subducts the less dense crust or plate. The ocean crust with a lower density floats "higher" than the heavier more dense oceanic crust. Because the oceanic crust is heavier and more dense, the oceanic crust if forced underneath Continental crust creating what is know as a Subduction zone. Just like in the previous example, the more dense oceanic crust subducts and gets forced underneath, melting in the Subduction zone from the immense pressure and friction between the two plates. As a result the subducting plate or crust melts and becomes magma. This Magma higher is higher in temperature (hotter) and less dense than the surrounding rock and therefore floats to the surface through cracks and fissures. As the magma continues to rise up through the cracks,it escapes onto the surface and solidifies, building up chain of Volcanic Islands at the surface over Millions of years. Magma on the surface is now known as lava. The converging of the oceanic and continental plate also cause deep oceanic trenches to form. Japan, Indonesia, and the Marianas Islands are all examples of a chain of volcanic islands that formed at Ocean to Ocean convergent plate boundary.
Convergent: Continent--><--Continent
When two continents meet head-on, neither plate or crust is subducted because the continental rocks are relatively light and have the same density, like two colliding icebergs, these plates resist downward motion and therefore do not subduct. Instead, the crust tends to buckle and be pushed upward building mountains. The collision of India into Asia 40 million years ago caused the Eurasian Plate to crumple up and override the Indian Plate. After the collision, the slow continuous convergence of the two plates over millions of years pushed up the Himalayan Mountains to their present heights, creating the highest mountain in the world, Mount Everest.Divergent Plate Boundaries
Remember the theory of Seafloor Spreading? After the the theory of Plate Tectonics, Seafloor Spreading became known as a Divergent Plate Boundary. Plates move apart or separate at divergent plate boundaries. At Divergent Boundaries in the oceans, magma from deep in the Earth's mantle rises toward the surface and pushes apart two or more plates. This process is what was responsible for breaking up Pangaea 250 millions years ago. Mountains and volcanoes rise along an underwater system of volcanoes called Ocean Ridges. These Ocean ridges are areas of new crust or plate creation. As you move farther from the ridge, rock becomes older. The mid-Atlantic Ocean ridge system is a perfect example of a divergent plate boundary.This process creates new ocean floor rock at the ridges and pushes apart continents. A single mid-ocean ridge system connects the world's oceans, making the ridge the longest mountain range in the world. On land, divergent plate boundaries can break apart continents such as the Great Rift Valley in Africa, where plates are tugged apart. If the plates there continue to diverge, millions of years from now eastern Africa will split from the continent to form a new landmass. Eventually, East will be ripped apart from the rest of the African Continent, creating a linear sea and one day an ocean. A mid-ocean ridge would then mark the boundary between the plates. At almost every Divergent Plate boundary you find features such as Ocean ridges or a long continuous Valley know as rift valley. Active volcanism (volcanoes) occur at divergent plate boundaries along with frequent earthquakes.
Transform Plate Boundaries
The San Andreas Fault in California is an example of a Transform Plate Boundary, where two plates grind past each other along what are called strike-slip faults. At the San Andreas Transform plate Boundary, The pacific Plate grinds or slides past the North American Plate. These boundaries don't
Rafts of Rock
If you recall Alfred Wegener could not explain how continents or plates moved; and therefore his theory was rejected by fellow scientists. So what force couldpossibly be strong enough to move continents and the outer crust of our Earth? The answer come from heat within our Earth. Heat from the core fuelsor drives plate tectonics. Convection in the Mantle causes creates areas within our Earth' s where hot low density molten rock (magma) rises in certain locations, moving these plate the plates like giant rafts of rock. What goes up must come down right? Well, if you consider a lava lamp, as the that heated lava rises, eventually it will cool and sink back down. The same process happens within our Earth. Eventually this molten high density rock (magma) will cool and sink back down. This rising and sinking process creates convection currents within our Earth's mantle, a force strong enough to move plate, build mountains, release Earthquakes, and fuel the Volcanoes through our world.
Plate Tectonics Discussion Forum